Renewable fuels for U.S. military ships and jets are likely to remain “far more expensive” than petroleum products absent a technological breakthrough, a study for the U.S. Air Force found on Tuesday, questioning a Pentagon push for alternative energy.

The study by the RAND Corporation think tank said that while the U.S. Defense Department is a huge consumer of fuel at about 340,000 barrels per day, that figure is a tiny fraction of the 87 million barrels per day of global demand, too small to influence price significantly.

Efforts to make fuel from seed or algae oils are not producing at the scale or price necessary to meet the military’s demand at a reasonable cost, said James Bartis, the RAND researcher who authored a volume of the report.

If DoD is looking for places to save money, they might want to start looking here.